ISC Anti-Image Chassis (S1102755) found to have bad channel on one of the filter boards (D070081 Rev 5 SN S1106145) CH4. U1 output railing at 14V. Replaced filter boards: serial number S1106145(Rev5) and S1106146 (Rev5) with S1201597 (Rev6) and S1201598 (Rev6).